Traveling mechanisms with hydrostatic gear and multi-ratio change gear transmission are used in the modern construction and mobile machinery such as loaders, excavators or crawlers. A driving motor, particularly a diesel engine, drives a hydrostatic variable displacement pump which, together with the variable displacement motor, forms a hydrostatic transmission having a reduction ratio adjusted by a rotational-speed dependent control pressure. The subject is a rotational-speed dependent, automotive adjustment of the hydrostatic mechanism, i.e. pump and motor automatically regulate the reduction ratio, according to the rotational speed, and the load of the primary drive mechanism so that the reduction ratio increases as the load increases and decreases as the rotational speed increases. Together with the hydrostatic transmission, the driving device belongs to a power shiftable transmission in the form of a two-gear planetary transmission. Two auxiliary pumps, driven by the primary drive mechanism, a feed and control pump produce the system and control pressure. An auxiliary pump with the distributer system can also be used instead of the two auxiliary pumps. Electromagnetic valves control the pressurized fluid supply to the powershift elements which can be actuated pneumatically, hydraulically, electromagnetically or by springs.
In traveling mechanism systems for mobile machinery, several draft variants are distinguished. The different mechanism drafts are tailored to the corresponding main requirements. Thus, even though the dog clutch or sliding transmission shiftable when parking can be economically produced, they make gear shifts possible only when parking with unfavorable control comfort at the same time. On the other hand, it is possible by using hydrostatic summarizing transmissions with two or more hydromotors to obtain a relatively better traveling comfort. But the variant is comparatively expensive and has only a small conversion range, the same as an unfavorable degree of efficiency at high driving speeds. Likewise costly and requiring high expenditures, another solution is a combination gear with hydrostatic summarizing and rear-mounted power shift clutches. The shifting operations are carried always out in branches of the transmission that transmit no power. Power shiftable transmissions with continuously variable hydrostatic system combined with synchronized shifting sequences offer great traveling comfort, but are an uneconomical solution from the points of view of cost and efficiency.
A traveling mechanism with a hydrostatic transmission and a multi-ratio gear change transmission for mobile construction and working machinery has been disclosed in DE 44 31 864 A1, but the traveling mechanism is expensive due to the use of a powershift transmission.
The problem on which this invention is based is to produce an economical, simple driving solution which stands out by favorable efficiency ratios, relatively comfortable shifting sequences, even while driving, and the possibility of automatic shifting operations. Besides, it is suited to open and closed hydrostatic, hydraulic circuits and for slow and fast moving machines.
The problem on which the invention is based is solved by a traveling mechanism.